Thanks for your reply, by the looks of your answer you do understand what I'm trying to do, but it doesn't seem to be working. Below is the code I am using the first line works its the code to launch/run Rainlendar the second & Third is the show & hide

The functions are already created. They come with Rainlendar2.
After trying it by myself, first I think that the -e option wasn't working. Then, after going back until build 70... I "see" what I've been missing.

SOLUTION. You need to use:
LeftMouseUpAction=!Execute ["C:\Program Files (x86)\Rainlendar2\rainlendar2.exe -e Hotkey_Hide_Windows()"] <--- add the parenthesis after the function name